Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A method for transmitting control information to a wireless node includes
determining, by a communications controller, a region for the control
information in a subframe as at least one of a data region and a control
region of the subframe. The method also includes modulating, by the
communications controller, the control information, and mapping, by the
communications controller, the modulated control information onto
resources of the subframe according to the determined region. The method
further includes transmitting, by the communications controller, the
subframe to the wireless node.

Claims:

1. A method for transmitting control information to a wireless node, the
method comprising: determining, by a communications controller, a region
for the control information in a subframe as at least one of a data
region and a control region of the subframe; modulating, by the
communications controller, the control information; mapping, by the
communications controller, the modulated control information onto
resources of the subframe according to the determined region; and
transmitting, by the communications controller, the subframe to the
wireless node.

2. The method of claim 1, further comprising determining the region for
the control information in the subframe according to availability of the
resources in the subframe.

3. The method of claim 1, further comprising determining the region of
the control information in the subframe without consideration of a type
of the control information or a control channel type.

4. The method of claim 1, further comprising transmitting a first
indicator identifying the determined region to the wireless node.

5. The method of claim 4, further comprising transmitting the first
indicator using higher layer signaling.

6. The method of claim 5, further comprising transmitting the first
indicator using radio resource control signaling.

7. The method of claim 4, further comprising transmitting the first
indicator in a control channel.

8. The method of claim 7, further comprising transmitting the first
indicator in a common search space of the control region of the subframe.

9. The method of claim 7, further comprising transmitting the first
indicator in a system information block.

10. The method of claim 1, wherein the resources of the subframe
comprises resource elements.

11. The method of claim 1, wherein the resources of the subframe
comprises resource blocks.

12. The method of claim 1, further comprising determining the region for
the control information in the subframe according to a link quality
measurement.

13. The method of claim 1, further comprising determining the region for
the control information in the subframe according to a subframe index.

14. The method of claim 13, wherein there is a plurality of subframes,
and the method further comprises: allocating a first subset of the
plurality of subframes, wherein the subframes in the first subset include
control channels located in control regions of the subframes in the first
subset; and allocating a second subset of the plurality of subframes,
wherein the subframes in the second subset include control channels
located in data regions of the subframes in the second subset.

15. The method of claim 14, further comprising transmitting a second
indicator indicating the subframes in the second subset.

16. The method of claim 1, further comprising determining the region for
the control information according to a user equipment radio network
temporary identifier of the wireless node.

17. A method for receiving control information, the method comprising:
determining, at a wireless node, a region indicator identifying a region
for a control channel in a subframe as at least one of a data region and
a control region of the subframe; determining, at the wireless node, a
location of resources for the control channel in the subframe according
to the region indicator; and retrieving, at the wireless node, the
control information from the determined location.

19. The method of claim 18, further comprising receiving the region
indicator using higher layer signaling.

20. The method of claim 19, further comprising receiving the region
indicator using radio resource control signaling.

21. The method of claim 18, further comprising receiving the region
indicator in a second control channel.

22. The method of claim 21, further comprising receiving the region
indicator in a common search space of the control region of the subframe.

23. The method of claim 22, further comprising receiving the region
indicator in a system information block.

24. The method of claim 17, further comprising determining the region
indicator according to a subframe index of the subframe.

25. The method of claim 24, further comprising receiving a subframe
indicator of a subset of subframes including subframes with control
channels located in data regions of the subframes in the subset.

26. The method of claim 17, further comprising determining the region
indicator according to a user equipment radio network temporary
identifier of a wireless node.

27. The method of claim 17, wherein retrieving the control information
comprises demodulating the control information from the determined
location.

28. A communications controller comprising: a processor configured to
determine a region for control information in a subframe as at least one
of a data region and a control region of the subframe, to modulate the
control information, and to map the modulated control information onto
resources of the subframe according to the determined region; and a
transmitter operatively coupled to the processor, the transmitter
configured to transmit the subframe to a wireless node.

29. The communications controller of claim 28, wherein the transmitter is
configured to transmit an indicator identifying the determined region to
the wireless node.

30. The communications controller of claim 29, wherein the transmitter is
configured to transmit the indicator using higher layer signaling.

31. The communications controller of claim 30, wherein the transmitter is
configured to transmit the indicator using radio resource control
signaling.

32. The communications controller of claim 29, wherein the transmitter is
configured to transmit the indicator using a control channel.

33. The communications controller of claim 32, wherein the transmitter is
configured to transmit the indicator in a common search space of the
control region of the subframe.

34. The communications controller of claim 32, wherein the transmitter is
configured to transmit the indicator in a system information block.

35. The communications controller of claim 28, wherein the processor is
configured to determine the region for the control information according
to a link quality measurement.

36. The communications controller of claim 28, wherein the processor is
configured to determine the region for the control information according
to a subframe index.

37. The communications controller of claim 28, wherein the processor is
configured to determine the region for the control information according
to a user equipment radio network temporary identifier of the wireless
node.

38. A wireless node comprising a processor configured to determine a
region indicator identifying a region for a control channel in a subframe
as at least one of a data region and a control region of the subframe, to
determine a location of resources for the control channel in the subframe
according to the region indicator, and to retrieve control information
from the determined location.

39. The wireless node of claim 38, further comprising a receiver
operatively coupled to the processor, the receiver configured to receive
the region indicator from a communications controller serving the
wireless node.

40. The wireless node of claim 39, wherein the receiver is configured to
receive the region indicator using higher layer signaling.

41. The wireless node of claim 39, wherein the receiver is configured to
receive the region indicator in a second control channel.

42. The wireless node of claim 41, wherein the receiver is configured to
receive the region indicator in a common search space of the control
region of the subframe.

43. The wireless node of claim 42, wherein the receiver is configured to
receive the region indicator in a system information block.

44. The wireless node of claim 38, wherein the processor is configured to
determine the region indicator according to a subframe index of the
subframe.

45. The wireless node of claim 44, further comprising a receiver
operatively coupled to the processor, the receiver configured to receive
a subframe indicator of a subset of subframes including subframes with
control channels located in data regions of the subframes in the subset.

46. The wireless node of claim 38, wherein the processor is configured to
determine the region indicator according to a user equipment radio
network temporary identifier of a wireless node.

47. The wireless node of claim 38, wherein the processor is configured to
demodulate the control information from the determined location.

Description:

[0001] This application claims the benefit of U.S. Provisional Application
Nos. 61/470,940, filed on Apr. 1, 2011, entitled "System and Method for
Transmission and Reception of Control Channels in a Communications
System," No. 61/471,049, filed on Apr. 1, 2011, entitled "System and
Method for Signaling a Location of a Control Channel," No. 61/471,055,
filed on Apr. 1, 2011, entitled "System and Method for Transmission and
Reception of Control Channels," and No. 61/471,061, filed on Apr. 1,
2011, entitled "System and Method for Transmission and Reception of
Control Channels," which applications are hereby incorporated herein by
reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is related to the following co-assigned patent
application Ser. No. ______, filed ______, Attorney Docket Number HW
83138110US06, entitled "System and Method for Signaling a Location of a
Control Channel"; Ser. No. ______, filed ______, Attorney Docket Number
HW 83138110US07, entitled "System and Method for Transmitting and
Receiving Control Channels"; and Ser. No. ______, filed ______, Attorney
Docket Number HW 83138110US08, entitled "System and Method for
Transmission and Reception of Control Channels" which applications are
hereby incorporated herein by reference.

TECHNICAL FIELD

[0003] The present disclosure relates generally to digital communications,
and more particularly to a system and method for transmission and
reception of control channels in a communications system.

BACKGROUND

[0004] Wireless telephony systems have traditionally been deployed using
the concept of a cell, with one base station (BS) (also known as base
transceiver station (BTS), Node B (NB), evolved NB (eNB), Access Point,
communications controller, and the like) covering a given geographic
area. BSs having the same or similar transmit power are typically used.
In addition, in order to maximize coverage and to maintain interference
at a reasonable level, careful site planning is used. A network deployed
in such a manner is usually referred to as a homogenous network
(HomoNet).

[0005] While such a deployment is optimal when the user density is
uniform, in practice, it has serious shortcomings because the user
density and traffic demand are rarely uniform. For example, in rural
areas, roads are typically the only area where users are present. In
urban or suburban areas, there are locations (hot spots) where the
traffic demand is higher: such locations may comprise shopping malls,
hotels, conference centers, and the like.

[0006] In order to improve coverage and user satisfaction, it may be
advantageous to cover these hot spots of traffic demands with Low Power
Nodes (LPNs). For instance, lower power base stations can be deployed to,
e.g., cover lobbies of hotels, portions of shopping malls, and the like.
The coverage of such a base station is referred to as a pico cell. When
the base station transmit power is even lower, e.g., to cover a single
residential unit, the coverage of such a base station is referred to as a
femto cell. A network comprising regular base stations and pico cells
and/or femto cells is referred to as a heterogeneous network (HetNet).

[0007] HetNets present new challenges to the deployment of a cellular
system. In particular, the cellular layout may not be as regular as for a
HomoNet since it is dependent on the hot spot locations. In particular,
it may well happen that a LPN is located close to another base station.
The close proximity can create a high level of interference for both user
equipment (UE) (also known as mobile station (MS), terminal, user,
subscriber, wireless node, and the like) and BSs.

[0008] In the Third Generation Partnership Project (3GPP) Long Term
Evolution (LTE) Release-10 technical standards, transmissions from the BS
comprise both data channels and control channels. The interference can
affect both the data channels and control channels. While solutions exist
to mitigate interference on the data channels, no such solution has been
defined yet for the control channels.

SUMMARY OF THE DISCLOSURE

[0009] Example embodiments of the present disclosure which provide a
system and method for transmission and reception of control channels in a
communications system.

[0010] In accordance with an example embodiment of the present disclosure,
a method for transmitting control information to a wireless node is
provided. The method includes determining, by a communications
controller, a region for the control information in a subframe as at
least one of a data region and a control region of the subframe. The
method also includes modulating, by the communications controller, the
control information, and mapping, by the communications controller, the
modulated control information onto resources of the subframe according to
the determined region. The method further includes transmitting, by the
communications controller, the subframe to the wireless node.

[0011] In accordance with another example embodiment of the present
disclosure, a method for receiving control information is provided. The
method includes determining, at a wireless node, a region indicator
identifying a region for a control channel in a subframe as at least one
of a data region and a control region of the subframe. The method also
includes determining, at the wireless node, a location of resources for
the control channel in the subframe according to the region indicator,
and retrieving, at the wireless node, the control information from the
determined location.

[0012] In accordance with another example embodiment of the present
disclosure, a communications controller is provided. The communications
controller includes a processor, and a transmitter operatively coupled to
the processor. The processor determines a region for control information
in a subframe as at least one of a data region and a control region of
the subframe, modulates the control information, and maps the modulated
control information onto resources of the subframe according to the
determined region. The transmitter transmits the subframe to a wireless
node.

[0013] In accordance with another example embodiment of the present
disclosure, a wireless node is provided. The wireless node includes a
processor. The processor determines a region indicator identifying a
region for a control channel in a subframe as at least one of a data
region and a control region of the subframe, determines a location of
resources for the control channel in the subframe according to the region
indicator, and retrieves control information from the determined
location.

[0014] One advantage of an embodiment is that a U-PDCCH control region may
be used to mitigate interference on the DL.

[0015] A further advantage of exemplary embodiments is that the U-PDCCH
control region may be designed to manage interference in a Heterogeneous
Network (HetNet) deployment or in a Cooperative Multipoint (CoMP)
deployment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a more complete understanding of the present disclosure, and
the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawing, in
which:

[0017] FIG. 1 illustrates an example communications system according to
example embodiments described herein;

[0019] FIGS. 3a through 3e illustrate example locations for a second
control region in a data region according to example embodiments
described herein;

[0020] FIG. 3f illustrates an example HetNet communications system
configured with fixed assignment of U-PDCCH to UEs according to example
embodiments described herein;

[0021] FIG. 3g illustrates an example HetNet communications system
configured with flexible assignment of U-PDCCH to UEs according to
example embodiments described herein;

[0022] FIG. 4a illustrates an example flow diagram of eNB operations in
notifying a UE to monitor a PDCCH control region or a U-PDCCH control
region or both control regions according to example embodiments described
herein;

[0023] FIG. 4b illustrates an example flow diagram of UE operations in
monitoring either a PDCCH control region or a U-PDCCH control region or
both control regions according to example embodiments described herein;

[0024] FIG. 4c illustrates an example flow diagram of eNB operations in
selecting a region for a control channel according to example embodiments
described herein;

[0025] FIG. 5a illustrates an example flow diagram of eNB operations in
switching a UE from monitoring a PDCCH control region to a U-PDCCH
control region according to example embodiments described herein;

[0026] FIG. 5b illustrates an example flow diagram of UE operations in
switching from monitoring a PDCCH control region to a U-PDCCH control
region according to example embodiments described herein;

[0027] FIG. 6a illustrates an example flow diagram of eNB operations for
controlling the control channel monitoring of a UE according to example
embodiments described herein;

[0028] FIG. 6b illustrates an example flow diagram of UE operations for
monitoring of a control channel by a UE according to example embodiments
described herein;

[0029] FIG. 7a illustrates an example flow diagram of eNB operations in
switching a UE from monitoring a PDCCH control region to a U-PDCCH
control region with implicit acknowledgement according to example
embodiments described herein;

[0030]FIG. 7b illustrates an example flow diagram of UE operations in
switching from monitoring a PDCCH control region to a U-PDCCH control
region with implicit acknowledgement according to example embodiments
described herein;

[0031] FIG. 8 illustrates an example flow diagram of UE operations in
switching from monitoring a PDCCH control region to a U-PDCCH control
region with implicit acknowledgement based on power measurements
according to example embodiments described herein;

[0032] FIG. 9 illustrates an example flow diagram of eNB operations in
switching a UE from monitoring a PDCCH control region to a U-PDCCH
control region with implicit acknowledgement based on power measurements
according to example embodiments described herein;

[0033] FIG. 10 illustrates an example flow diagram of eNB operations in
switching a UE from monitoring a PDCCH control region to a U-PDCCH
control region on a subframe by subframe basis according to example
embodiments described herein;

[0034] FIG. 11 illustrates an example flow diagram of UE operations in
switching from monitoring a PDCCH control region to a U-PDCCH control
region on a subframe by subframe basis according to example embodiments
described herein;

[0035] FIG. 12 illustrates an example flow diagram of eNB operations in
switching a UE from monitoring a PDCCH control region to a U-PDCCH
control region with a dynamic trigger according to example embodiments
described herein;

[0036] FIG. 13 illustrates an example flow diagram of UE operations in
switching from monitoring a PDCCH control region to a U-PDCCH control
region with a dynamic trigger according to example embodiments described
herein;

[0039] FIG. 16 illustrates locations of example U-PDCCHs within a new
control region according to example embodiments described herein; and

[0040] FIG. 17 illustrates an example flow diagram of UE operations in
searching for U-PDCCH using a PCFICH according to example embodiments
described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0041] The operating of the current example embodiments and the structure
thereof are discussed in detail below. It should be appreciated, however,
that the present disclosure provides many applicable inventive concepts
that can be embodied in a wide variety of specific contexts. The specific
embodiments discussed are merely illustrative of specific structures of
the disclosure and ways to operate the disclosure, and do not limit the
scope of the disclosure.

[0042] One embodiment of the disclosure relates to transmission and
reception of control channels in a communications system. For example, an
eNB selects a region and transmits a first control channel in a first
control region and/or a second control channel in a second control
region. The first control region and the second control region may be
part of a single subframe. The first control region and the second
control region may be part of different subframes. The eNB may transmit
sequences of subframes, with a first sequence of subframes including only
first control channels and no second control channels, a second sequence
of subframes including only second control channels and no first control
channels, and a third sequence of subframes including both first control
channels and second control channels. Each subframe in the sequences of
subframes includes an indicator that indicates which control channel (or
both) is transmitted.

[0043] The present disclosure will be described with respect to example
embodiments in a specific context, namely a HetNet deployment including a
3GPP LTE compliant communications system. The disclosure may also be
applied, however, to other HetNet deployments, such as those including
3GPP LTE-Advanced, WiMAX, and the like, compliant communications systems,
as well as HetNet deployments with non-standards compliant communications
systems.

[0044] For 3GPP LTE Release 10 (Release-10) and earlier technical
standards, both a Physical Downlink Control Channel (PDCCH) and a
Physical Downlink Shared Channel (PDSCH) are defined. The PDSCH may be
used to carry data information. The PDCCH may convey control information
about a particular PDSCH, such as resource allocation information,
modulation and coding information, and information about a Physical
Uplink Shared Channel (PUSCH). The PDCCH may be considered to be a first
type of control channel. For brevity, the control information for PDSCH
and PUSCH can be referred as resource allocation information.

[0045] The PDCCH may be located in the first several symbols (e.g., one to
four symbols) of a subframe. These PDCCH-bearing symbols may be referred
to as a control domain or a control region. Other symbols in the subframe
may be used for data transmission, and may be referred to herein as a
data domain or a data region. Hence the PDCCH is located in control
region while the PDSCH is located in data region.

[0046] In the control region, there may be other control channels, such as
a Physical Hybrid Indicator Channel (PHICH), which is used to transmit
ACK/NACK in response to uplink data transmission, and the Physical
Control Format Indicator Channel (PCFICH), which is used to indicate the
number of symbols of a control region in a subframe.

[0047] In 3GPP LTE Release-11 (LTE-A) or beyond technical standards, an
eNB locates a new type of control channel(s), which may be located in the
data region, control region, or both of a subframe may be considered.
More specifically, when the control channel is located in the data
region, a second control region may be defined and uses a portion of the
data region. The second control region comprising some combination of
time and frequency resources, e.g., resource elements, with a group of
resource elements forming a resource block (RB). For example, in one 3GPP
LTE configuration, 84 resource elements make up a RB. Similarly, a group
of resource elements forms a control channel element. For example, in one
3GPP LTE configuration, 36 resource elements make up a control channel
element. At least part of the time and frequency resources (or simply,
resources) of the second control region may be used for transmitting
control information in the new type of control channel, e.g., a second
type of control channel. The resources of the second control region that
are not used for transmitting control information may be used for other
purposes, such as transmitting data, e.g., on the PDSCH.

[0048] One or more resource elements or parts of resource blocks (RBs)
from the data region may be allocated for the second control region. As
an example, a new second type control channel, a UE Physical Downlink
Control Channel (U-PDCCH), may be located in the second control region of
the data region (or the control region or both the data region and the
control region), and may carry control information for a PDSCH channel or
control information for a PUSCH channel. The second channel may carry
resource assignments for UEs or other network nodes such as relay nodes.
Additionally, the second control region may carry channels analogous to
those carried in the first control region, such as the physical hybrid
automatic repeat requested indicator channel (PHICH), and the like. A
prefix of "U-" may be added to indicate the analogous channel in the
second control region, such as the "U-PHICH". Collectively, information
carried in these control channels, such as resource assignments (also
commonly referred to as resource allocation assignments), configuration
information, power control, codebook information, hybrid automatic repeat
requested (HARQ) information, and the like, may be referred to as control
information. The format and content of these analogous channels may be
different from the first control region.

[0049] In addition to the first type of control channel and the second
type of control channel, there may be other control channel types,
including a third type of control channel, which may be transmitted in
both the first control region and in the second control region. The
information in the two control regions may be the same or it may be
different.

[0050] FIG. 1 illustrates a communications system 100. Communications
system 100 includes an evolved NodeB (eNB) 105, which may also be
commonly referred to as a controller, a communications controller, a base
station, a NodeB, and the like. Communications system 100 also includes a
plurality of User Equipment (UE), such as UE 110, 112, and 120. A UE may
also be commonly referred to as a mobile, mobile station, subscriber,
user, terminal, wireless node, and the like. In addition, the
communication system may include other entities such as Relay Node (RN)
115. The RN may serve one or more UEs, such as UE 120.

[0051] Communications between eNB 105 and a given UE may occur over a link
that comprises a Un downlink (DL) channel and an Un uplink (UL) channel.
UEs not directly served by the RN and RNs may be multiplexed together
using and may be allocated different RBs. For 3GPP LTE Release-10, the UE
resource assignments are transmitted on the PDCCH.

[0052] While it is understood that communications systems may employ
multiple eNBs capable of communicating with a number of UEs, only one
eNB, a plurality of UEs, and one RN are illustrated for simplicity.

[0053] FIG. 2a illustrates a first subframe 200. Subframe 200 comprises a
first control region 205 and a data region 210. Subframe 200 shows an
example for a multicarrier modulation system. As discussed above, first
control region 205 may include control signaling, such as a PDCCH, while
data region 210 may include data as well as control signaling, which may
include a PDSCH, as well as new control channels, such as a U-PHICH or a
U-PDCCH.

[0054] First control region 205 may also be called a PDCCH control region
and may contain the first type of control channels. The new control
channels (e.g., the second type of control channels) are located in a new
control region 215 (also commonly referred to as a second control region
215), which may be inside data region 210. New control region 215 can
also be called the U-PDCCH control region. Although data region 210 may
be used to transmit data, no data is shown in FIG. 2a. As shown in FIG.
2a, second control region 215 is located in data region 210, while PDCCH
is located in first control region 205.

[0055] The representation of the various channels and regions in FIG. 2a
is logical in nature with no direct relationship to an actual mapping of
specific physical resources. In particular, the resources comprising
second control region 215 may be distributed in frequency and are not
restricted to be contiguous in frequency. Second control region 215 may
also be time multiplexed with data, and for instance, may occupy only the
first or the second slot of a subframe. In addition, second control
region 215 may not necessarily start immediately after first control
region 205, but may be offset by one or more symbols. Second control
region 215 may consist of Physical RBs (PRBs) or Virtual RBs (VRBs),
either localized or distributed. The PRBs and the VRBs comprise a
plurality of resource elements.

[0056] FIG. 2b illustrates a second subframe 230. Subframe 230 comprises a
first control region 235 and a data region 240. As discussed above, first
control region 235 may include control signaling, such as a PDCCH, while
data region 240 may include data without control signaling. First control
region 235 may also be called a PDCCH control region.

[0057] FIG. 2c illustrates a third subframe 260. Subframe 260 comprises a
data region 265. As discussed above, data region 265 may include data as
well as control signaling, which may include a PDSCH, as well as new
control channels, such as a U-PDCCH or a U-PHICH. The new control
channels are located in a new control region 270, which may be inside
data region 265. New control region 270 may be used to transmit data, but
no data is shown in FIG. 2c. As shown in FIG. 2c, new control region 270
is located in data region 265. It is noted that subframe 260 has no PDCCH
since a first control region is absent.

[0058]FIG. 2d illustrates a fourth subframe 280. Subframe 280 comprises a
control region 285 and a data region 290. As discussed above, control
region 285 may include control signaling, while data region 290 may
include data as well as control signaling. The new control channel may be
located in a first new control region 292, which may be inside control
region 285, as well as in a second new control region 294, which may be
inside data region 290.

[0059] In 3GPP LTE Release-10 and previous releases, a search space may be
used to define possible locations for a PDCCH within the PDCCH control
region. The PDCCH control region comprises one or more control channel
elements (CCEs). There is a mapping procedure for assigning the resource
elements that comprise each CCE to a both time location and frequency
location, i.e., resources, within the PDCCH control region. A particular
PDCCH may occupy 1, 2, 4, or 8 consecutive CCEs. A UE may use search
space rules to identify possible CCEs that contain control information,
such as, resource assignments (i.e., a PDCCH), for it. The search space
rules may also have provisions for a common search space.

[0060] FIG. 3a illustrates a diagram of possible locations for a second
control region in a data region 310 of a subframe. Also shown in FIG. 3a
is a first control region 305. Data region 310 comprises one or more RBs
(each of which comprises a plurality of resource elements or a plurality
of control channel elements) in the first slot (RBs 330, 331, 332, 333,
and 334) and one or more RBs in the second slot (RBs 335, 336, 337, 338,
and 339). In FIG. 3a, examples of adjacent RBs in the first slot are 330
and 331, 331 and 332, and the like. Similarly, examples of adjacent RBs
in the second slot are 336 and 337, 338 and 339, and the like.

[0061]FIG. 3b illustrates an example U-PDCCH control region within data
region 310 of a subframe, with the U-PDCCH control region occupying
adjacent RBs. As shown in FIG. 3b, the U-PDCCH control region may occupy
adjacent RBs, such as 331, 332, 333, 336, 337, and 338 for U-PDCCH 320.
FIG. 3c illustrates an example U-PDCCH control region with data region
310 of a subframe, with the U-PDCCH control region occupying distributed
VRBs. As shown in FIG. 3c, the U-PDCCH control region may occupy
distributed VRBs using 330, 332, 334, 335, 337, and 339 for U-PDCCH 321.

[0062]FIG. 3d illustrates an example U-PDCCH control region within data
region 310 of a subframe, with the U-PDCCH control region occupying first
slot RBs. As shown in FIG. 3d, the U-PDCCH control region may occupy the
first slot using RBs 331, 332, and 333 for U-PDCCH 322. FIG. 3e
illustrates an example U-PDCCH control region within data region 310 of a
subframe, with the U-PDCCH control region occupying second slot RBs. As
shown in FIG. 3e, the U-PDCCH control region may occupy the second slot
using 336, 337, and 338 for U-PDCCH 323. It is also noted that the
U-PDCCH control region may occupy RBs that are combinations of those
illustrated herein. It is noted that although first control regions are
shown in FIGS. 3a through 3e, in some subframes, the first control region
may be absent.

[0063] In a communications system with relay nodes, a R-PDCCH may be used
to transmit control signaling for notifying RNs of the DL and/or UL
grants on the Un link (the link between the eNB and the RN). However, the
R-PDCCH may have limitations if it were used for UEs. The R-PDCCH may be
used as a basis for designing a new control channel (herein referred to
as a U-PDCCH) to allow UEs to be notified of their UL and/or DL grants.

[0064] There are some benefits of having a U-PDCCH and/or a U-PHICH. The
U-PDCCH and the U-PHICH, as well as other control channels located in the
data region (i.e., the second control region), may be referred to as data
region control channels. For example, different cells may allocate
orthogonal time-frequency resource (different second control regions) for
the U-PDCCH and/or U-PHICH, thus the interference between U-PDCCH and/or
U-PHICHs of different cells is significantly lowered. Another benefit may
be that a dedicated reference signal can be used for the second control
region, in other words, second control region has its own reference
signal for channel estimation during demodulation, thereby allowing more
advanced transmission schemes, such as beam forming or precoding.

[0065] There are some benefits of having a PDCCH and a U-PDCCH and/or a
U-PHICH. The PDCCH may be detectable by legacy UEs, which would not be
able to detect the U-PDCCH and/or a U-PHICH. Furthermore, the ability to
distribute some of control information to the U-PDCCH and/or the U-PHICH
may enable the eNB to perform load balancing on the different control
channels. Additionally, if the transmission of control information on a
particular control region (e.g., the first control region or the second
control region (i.e., the data region)) is failing, it may be possible to
use a different control region to potentially achieve better transmission
performance,

[0066] Several properties make the U-PDCCH control region (the second
control region or the data region) an attractive solution to mitigate the
effects of interference on the DL:

[0067] 1. A U-PDCCH control region may occupy a subset of frequency
resources, thereby providing orthogonality for control channels in
frequency domain from different HetNet layers unlike other time division
multiplex (TDM) HetNet solutions (e.g., almost blank subframe (ABS))
which may provide orthogonality in time domain;

[0068] 2. A U-PDCCH control region does not disrupt or conflict with the
current physical data control channel (i.e., a PDCCH), so prior release
UEs (i.e., legacy UEs) are not impacted and are without a reduction in
peak data rate if the resource allocation of the U-PDCCH control region
can be released dynamically which may be a problem with other frequency
division multiplex (FDM) HetNet solutions;

[0069] 3. With a U-PDCCH control region, it may be possible to reduce the
number of symbols used for a PDCCH control region, thus to improve the
overall capacity (e.g., the time granularity is 1/14th in time with a
normal cyclic prefix (CP), but can be much lower in frequency, e.g.,
1/50th for a 10 MHz deployment); and

[0070] 4. It may be possible to use a Demodulation Reference Signal (DMRS)
on the U-PDCCH control region. The use of the DMRS could create a more
efficient control channel that may take advantage of technologies such as
dynamic link adaptation, frequency selective resource allocation, and
Multiple Input, Multiple Output (MIMO) transmission. Some of these
improvements can be done for the PDCCH (e.g., link adaptation), but, for
example, Multi-User MIMO (MU-MIMO) is better suited for the U-PDCCH.

[0071] Comparing to a backhaul link between a Donor eNB (DeNB) and the
Relay Node (RN), there may be some unique properties of the access link
between the eNB and the UE and hence some issues that should be
considered:

[0072] a) A UE is generally mobile while a RN is typically stationary.
This implies that fast link adaptation is more beneficial and desirable,
and at the same time more difficult. A difficulty is due to the lack of
another control channel to inform the transmission format of U-PDCCH as
in the case of PDSCH. Another related issue is that due to mobility of
the UE, the re-transmission rate for PDSCH of a UE tends to be higher
than that of a RN;

[0073] b) A UE may read a PDCCH while a RN cannot. Therefore, PDCCH and
U-PDCCH may co-exist for a UE and designs are needed to cope with and
take advantage of the co-existence;

[0074] c) Since the number of UEs associated with a cell is typically be
much larger than the number of RNs, a more efficient design of the
U-PDCCH may be required to reduce overhead and ensure high performance;

[0075] d) Because the location of a RN can be carefully selected, it
generally sees better channel quality compared to a UE. Therefore, there
is a higher requirement for interference management for the UE,
especially for the control channel; and

[0076] e) No switching time is needed for a UE as in the case of RN.

[0077] The following is a discussion of exemplary scenarios illustrating
the attractiveness of a U-PDCCH.

[0078] Scenario 1: HetNet Deployment

[0079] A HetNet deployment typically has an aggressor layer and a victim
layer. At a given location in a deployment, the power received from an
aggressor layer may be much greater than the power received from the
victim layer. As an example, in a first deployment, a macro layer may be
considered an aggressor to a victim pico layer. Alternatively, in a
second deployment, a femto layer may be considered an aggressor to a
victim macro layer. Taking as an example the macro-pico HetNet deployment
scenario as described above, the macro cell layer may use the regular
PDCCH as specified in 3GPP LTE Release-10. Data for macro-UEs, which are
UEs assigned to a macro cell layer, can be scheduled anywhere in the data
region. For example, to mitigate interference, power control can be
applied on the downlink control channels so that low-power transmissions
can be used for macro UEs. As a result, the macro cell layer can have a
PDCCH for each subframe while the pico cell layers can use either PDCCH
or U-PDCCH. It is noted that this is just one of many possible scenarios.
For other scenarios, it can be beneficial for the macro layer to have a
U-PDCCH as well.

[0080] Scenario 1a: Fixed Assignment of U-PDCCH to UEs

[0081] In scenario 1a, pico-UEs, i.e., UEs assigned to a pico cell layer,
are assigned one control channel only. Some UEs receive their assignments
on the U-PDCCH only while other UEs receive their assignment on the
regular PDCCH. The latter case may be needed for legacy UEs, for example.
The pico eNB needs to transmit at least a common reference signal (CRS)
on the PDCCH, with possibly more information, similar to Almost Blank
Subframes (ABS). It is noted that the U-PDCCH may be interfered with by a
reference signal (RS) sent by the macro cell. Muting and/or puncturing
may be needed to mitigate the interference. FIG. 3f illustrates a HetNet
communications system configured with a fixed assignment of U-PDCCH to
UEs.

[0082] Scenario 1b: Flexible Assignment of U-PDCCH to UEs

[0083] In scenario 1b, the pico UEs may receive assignments either on the
PDCCH or the U-PDCCH. For instance, pico UEs severely interfered by the
macro cell's PDCCH may switch to the U-PDCCH while UEs having a
manageable level of interference (e.g., UEs close to the pico cell) may
continue to use the PDCCH. It is noted that the dynamic switching
mechanism may also be useful to perform load balancing on the control
channel region, for example. FIG. 3g illustrates a HetNet communications
system configured with flexible assignment of U-PDCCH to UEs.

[0084] Scenario 2: CoMP Deployment

[0085] In scenario 2, the U-PDCCH may be used to avoid a potentially high
level of interference between the PDCCH from two cells. A PDCCH in a
first cell and a U-PDCCH in a second cell may be made orthogonal to help
reduce interference. Orthogonalization is discussed in greater detail
below. As in scenarios 1a and 1b discussed previously, fixed assignment
and flexible assignment of the U-PDCCH may be used.

[0086] In some scenarios, both PDCCH and U-PDCCH may coexist in a single
cell and are transmitted by the same eNB (e.g., scenario 1a discussed
above). Therefore, there may be a need for protocol and signaling to a UE
to have the UE switch from monitoring the PDCCH control region to
monitoring the U-PDCCH control region and vice versa.

[0087] FIG. 4a illustrates a flow diagram of eNB operations 400 in
notifying a UE to monitor a PDCCH control region or a U-PDCCH control
region or both control regions. eNB operations 400 may be indicative of
operations occurring in an eNB, such as eNB 105, as the eNB notifies a UE
to monitor a PDCCH control region or a U-PDCCH control region or both
control regions.

[0088] eNB operations 400 may begin with the eNB selecting a region for a
control channel to use to transmit control information, such as a
resource allocation, to the UE (block 405). As discussed above, the
control channel may be located in a data region, a control region, or
both the data region and the control region. A control channel type may
indicate the region of the control channel. As discussed previously,
there may be a number of different control channel types. As an example,
there may be a first control channel type where the control channels are
transmitted in a first control region of a subframe. There may also be a
second control channel type where the control channels are transmitted in
a second control region of the subframe, i.e., in a data region of the
subframe. There may also be a third control channel type where the
control channels are transmitted in both the first control region and the
second control region of the subframe.

[0089] As an example, the eNB may select the region of the control
information according to availability of resources in the subframe. As
another example, the eNB may select the region of the control information
with or without consideration of a type of control information. As
another example, the eNB may select the region of the control information
with or without consideration of a type of the control channel.

[0090] The eNB may then transmit the control information, e.g., resource
allocation (or resource allocation information), to the UE. The
transmitting of the control information to the UE may include the eNB
modulating the control information according to a selected modulation
and/or coding scheme, such as Quadrature Phase Shift Keyed (QPSK), 16
Quadrature Amplitude Modulation (16-QAM), 64 Quadrature Amplitude
Modulation (64-QAM), and the like (block 410), mapping the modulated
control information to a plurality of resources, such as resource blocks,
control channel elements, or resource elements, where the modulated
control information may be mapped (e.g., assigned) to the plurality of
resources that are located in a portion of the subframe according to the
region (which may be indicated by the control channel type, for example)
selected by the eNB (block 415), and transmitting the subframe (block
420). As an example, if the eNB selected a first control region (e.g.,
indicated by a first control channel type), then the control information
may be located on a plurality of resources in the first control region,
while if the eNB selected a second control region (e.g., indicated by a
second control channel type), then the control information may be located
on a plurality of resources in the second control region, and if the eNB
selected both the first control region and the second control region
(e.g., indicated by a third control channel type), then the control
information may be located on a plurality of resources in both the first
control region and the second control region.

[0091] In addition to transmitting the control information to the UE, the
eNB may also transmit an indicator to the UE (block 425). As an example,
the indicator may identify a region for the control channel used to
transmit the control information to the UE. As another example, the
indicator may identify the type of the control channel used to transmit
the control information to the UE. For example, the indicator may
indicate that a first control channel type, a second control channel
type, or a third control channel type was used to transmit the resource
allocation to the UE.

[0092] FIG. 4b illustrates a flow diagram of UE operations 450 in
monitoring either a PDCCH control region or a U-PDCCH control region or
both control regions. UE operations 450 may be indicative of operations
occurring in a UE, such as UE 110 and UE 120, as the UE monitors either
the PDCCH control region or the U-PDCCH control region or both control
regions.

[0093] UE operations 450 may begin with the UE determining, e.g.,
receiving, an indicator (block 455). As an example, the indicator may
identify the region for a control channel used to transmit control
information to the UE. As another example, the indicator may indicate the
type of control channel used to transmit control information, e.g.,
resource allocation information to the UE. For example, the indicator may
indicate that a first control channel type, a second control channel
type, or a third control channel type was used to transmit the resource
allocation to the UE.

[0094] The UE may determine the location of the control channel in the
control region according to the indicator (block 460). As an example, if
the indicator identifies the region of the control channel, the UE may
know where in the subframe to look for the control channel. As another
example, if the indicator identifies that the first type of control
channel was used, then the UE knows that the resource allocation may be
found in the first control region. Similarly, if the second type of
control channel was used, then the UE knows that the resource allocation
may be found in the second control region, and if the third type of
control channel was used, then the UE knows that the resource allocation
may be found in both the first control region and the second control
region. The UE may retrieve, e.g., demodulate, information in the
resource elements in location of the control channel determined according
to the indicator (block 465). As an example, the UE may use a
demodulation and/or decoding scheme, such as QPSK, 16-QAM, 64-QAM, and
the like, to demodulate the information in the resource elements to
obtain the control information.

[0095] FIG. 4c illustrates a flow diagram of eNB operations in determining
a region for a control channel. eNB operations may be indicative of
operations occurring in an eNB, such as eNB 105, as the eNB determines a
region for a control channel in a subframe.

[0096] eNB operations may begin with the eNB determining a network
condition (block 485). As an example, the eNB may determine an error rate
of previous control channel transmissions in a first control region, a
second control region (i.e., a data region), and both the first control
region and the second control region. As another example, the eNB may
determine UE capability. As another example, the eNB may determine a load
on the control regions. As another example, the eNB may determine a link
quality or link condition (e.g., interference, signal to interference
plus noise ratio, signal to noise ratio, and the like), which may allow
or prevent the use of advance transmission techniques, such as beam
forming, precoding, and the like.

[0097] The eNB may select a region for the control channel according to
the network condition (block 487). As an example, if link quality or link
conditions allow the use of advanced transmission techniques (and if the
UE is capable), then the eNB may select the second control region to
transmit the control channel or both the first control region and the
second control region to transmit the control channel. As another
example, if the UE is not capable, then the UE may select the first
control region to transmit the control channel.

[0098] A solution may be to signal a UE to switch its monitoring between
the PDCCH control region and the U-PDCCH control region (and vice-versa)
using higher layer signaling, e.g., radio resource control (RRC)
signaling. As an example, an eNB may send a command to a UE to switch.
For instance, assume that eNB 105 wants to notify UE 120 to switch from
monitoring the PDCCH control region to the U-PDCCH control region.

[0099] FIG. 5a illustrates a flow diagram of operations 500 of an eNB as
the eNB notifies a served UE to switch the control region that it is
monitoring. Operations 500 may be indicative of operations occurring in
an eNB, such as eNB 105, as the eNB notifies a UE that it is serving to
monitor a different control region and a different control channel.

[0100] Operations 500 may begin with the eNB sending a resource assignment
to a UE, such as UE 120, using the PDCCH, located in the PDCCH control
region (block 510). The eNB may determine that there is a need to switch
the UE from the PDCCH control region to the U-PDCCH control region (block
512). The eNB may decide to switch the UE for several reasons including,
but not limited to performing load balancing between the two control
regions, or because a UE suffers from severe interference on its control
region. The eNB may send a dedicated RRC message (e.g., containing an
indicator) to the UE to notify the UE to switch to the U-PDCCH region
monitoring mode (block 514). As an example, the dedicated RRC message may
specify the UE should switch the control region that it is monitoring,
e.g., from the first control region to the second control region or from
the second control region to the first control region.

[0101] For subsequent resource assignments for the UE, the eNB may use the
U-PDCCH, located in the U-PDCCH control region, to send the resource
assignments (block 516). The operation from switching a served UE from
U-PDCCH monitoring to PDCCH monitoring is similar to what is described in
FIG. 5a for the eNB.

[0102] There are two search spaces in the PDCCH control region--one is a
UE-specific search space and the other is a common search space. The UE
may continue to monitor the PDCCH control region for PDCCH that are
assigned on the common search space even after it performs the switch of
the control channels. In this example, the switch is from the PDCCH in a
UE-specific search space within the PDCCH control region to the U-PDCCH.
After switching to the U-PDCCH, the UE may continue to monitor the common
search space in the PDCCH control region.

[0103] FIG. 5b illustrates a flow diagram of operations 550 of a UE as the
UE switches control region monitoring. Operations 550 may be indicative
of operations occurring at a UE, such as UE 120, as the UE switches
control region monitoring according to a notification from an eNB that is
serving the UE.

[0104] Operations 550 may begin with the UE receiving an assignment in the
PDCCH region (block 560). The UE may decode data received on resources
assigned in assignment received in block 560 (block 562), and the UE may
identify the message as RRC signaling to indicate that it is to start
monitoring the U-PDCCH control region (block 564). The UE may begin
monitoring the U-PDCCH control region for future resource assignments
(block 566). The operations for the UE switching from U-PDCCH monitoring
to PDCCH monitoring may be similar. It is noted also that the RRC message
may be sent over one or several frames. If received over several frames,
the UE may need to concatenate all received portions of the message
before decoding it, but operation is similar to that described in FIG.
5b.

[0105] Higher layer signaling may be attractive if switching is not a very
frequent occurrence. With higher layer signaling, there may be a time
ambiguity wherein there is latency between when the signaling switch is
commanded by the eNB and when the UE actually switches. Therefore, before
the UE explicitly acknowledges receipt of the higher layer signaling, the
UE may not be able to receive the PDCCH and/or the U-PDCCH for several
frames. During the time ambiguity, the UE may have to monitor both
control channels (the PDCCH and the U-PDCCH). The monitoring of both the
PDCCH and the U-PDCCH with a reduced search space may be a safe fallback
state. To help reduce performance overhead on the UE, a reduced search
space may be used to help ensure a constant requirement on a number of
blind decoding attempts performed by the UE.

[0106] Using both the PDCCH and the U-PDCCH may also be an option for a
normal mode of operation, i.e., the UE may monitor either the PDCCH or
the U-PDCCH or both the PDCCH and the U-PDCCH.

[0107] FIG. 6a illustrates a flow diagram of eNB operations 600 for
controlling the control channel monitoring of a UE. eNB operations 600
may be indicative of operations in an eNB, such as eNB 105, as the eNB
controls the monitoring of control channels by a UE.

[0108] The eNB may instruct the UE to monitor a U-PDCCH (or a PDCCH or
both the PDCCH and the U-PDCCH) (block 605). The eNB may instruct the UE
by sending a higher layer signaling message, such as with a RRC message.
Alternatively, the eNB may instruct the UE to switch the control channel
it is monitoring, e.g., if the UE is monitoring a PDCCH, then the UE
switches to the U-PDCCH, while if the UE is monitoring the U-PDCCH, then
the UE switches to the PDCCH and the U-PDCCH, while if the UE is
monitoring the PDCCH and the U-PDCCH, then the UE switches to the PDCCH.
It is noted that other switching sequences may be possible, as long as
both the eNB and the UE know the switching sequence to be used.

[0109] In order to handle time ambiguities and to allow the UE time to
switch, the eNB may continue for a period of time to send assignments on
both the PDCCH and the U-PDCCH (block 610). Once the eNB receives an
acknowledgement from the UE (block 615) as indicated by `Y`, the eNB may
continue to send assignments only on the U-PDCCH (or the PDCCH if the UE
is monitoring the PDCCH) (block 620). A timer can be used to measure the
period of time.

[0110] FIG. 6b illustrates a flow diagram of UE operations 650 for
monitoring of a control channel by a UE. UE operations 650 may be
indicative of operations occurring in a UE, such as UE 110 and UE 120, as
the UE monitors control channels.

[0111] UE operations 650 may begin with the UE monitoring the PDCCH, which
may be a system default (block 655). Upon receiving a message from the
eNB which may tell it which control channel to monitor (e.g., the PDCCH,
the U-PDCCH, or both the PDCCH and the U-PDCCH) or to simply switch the
control channel it is monitoring (block 660), the UE may handle time
ambiguities inherent in higher layer signaling by monitoring both the
PDCCH and the U-PDCCH regardless of the actual instruction from the eNB,
as an example (block 665).

[0112] The UE may continue monitoring both the PDCCH and the U-PDCCH until
it receives an assignment on the U-PDCCH (or whichever control channel
specified by the eNB) (block 670) as indicated by `N`. After receiving
the assignment as indicated by `Y`, the UE may send an acknowledgement to
the eNB (block 675).

[0113] It is noted that the acknowledgement from the UE may not
necessarily be needed. For example, the eNB may use both the U-PDCCH and
the PDCCH for a given period of time and then stop using both control
channels once the period of time expires. A timer can be used to
determine whether a period of time has expired, thereby negating the need
for the acknowledgement. As an example, the timer may be set to be equal
to (or greater than by an adjustable factor) a period of time that is
typical for the period of ambiguity involved RRC signaling.

[0114] The acknowledgement may be signaled in an implicit manner. The
PDCCH and U-PDCCH may contain different resource assignments, so an
acknowledgement for a DL transmission or receiving correctly an UL
transmission may indicate that the switch occurred correctly, as an
example.

[0115] FIG. 7a illustrates a flow diagram of eNB operations 700 in an eNB
for making assignments on control channels. eNB operations 700 may be
indicative of operations occurring in an eNB, such as eNB 105, as the eNB
makes assignments to UEs on control channels.

[0116] eNB operations 700 may begin with an eNB, such as eNB 105, sending
an assignment to a UE, such as UE 120, for a first message on the PDCCH
(block 710). The eNB may also send a second assignment to the UE for a
second message on the U-PDCCH (block 715). It is noted that the content
of the two messages may be the same, but they may be carried on different
network resources and have a different packet IDs, for example. The eNB
may then monitor for received acknowledgements (block 720). If an
acknowledgement is received for the second message as indicated by `Y`,
the eNB may then know that the UE has decoded the U-PDCCH, thus has
correctly processed the RRC signaling to switch channels. The eNB then
sends subsequent resource assignment on the U-PDCCH (block 725). If an
acknowledgement was not received as indicated by `N`, the eNB continues
sending dual assignments by returning to block 710.

[0117] It is noted that in the above description, the received
acknowledgment may not imply a packet acknowledgement, but may instead be
an indication that the assignment has been received by the UE. For
example, if the second message for packet I is not correctly decoded by
the UE, the UE may send a negative acknowledgment (NACK) for packet I.
Upon receiving the NACK, the eNB may be aware that the second assignment
was received correctly by the UE because the UE would not transmit an
acknowledgement (ACK) or NACK if it did not receive an assignment for
packet I. After receiving the NACK, the eNB may stop sending assignments
for that particular UE on the PDCCH, and may use the U-PDCCH only.

[0118] As an example, which control channel to be monitored by a UE is UE
specific by default. However, this information may also be configured as
a combination of a cell default in a system information block (SIB) and a
UE specific override. A control message sent on a SIB may be used to
signal to a UE to switch its monitoring of the PDCCH to the U-PDCCH and
vice-versa. When a control message on a SIB is used, either the U-PDCCH
or the PDCCH is needed to schedule the control message, i.e., provide
allocation information to the UE.

[0119]FIG. 7b illustrates a flow diagram of eNB operations 750 in an eNB
as the eNB specifies which control region is monitored by a UE. eNB 750
may be indicative of operations occurring in an eNB, such as eNB 105, as
the eNB uses a SIB to specify which control region a UE monitors.

[0120] eNB operations 750 may begin with the eNB sending assignments on
the PDCCH for UEs monitoring the PDCCH, and on the U-PDCCH for UEs
monitoring the U-PDCCH (block 760). The eNB may then send an assignment
on the PDCCH for a SIB that instructs the UEs monitoring the PDCCH to
switch to the U-PDCCH monitoring (block 765). The SIB assignment may be
sent in the common search space of the PDCCH control region. The eNB may
then send assignments to the UEs that were formerly monitoring the PDCCH
on the U-PDCCH (block 770). In order to provide a measure of robustness,
each UE may acknowledge that it has received the SIB, either with an
explicit acknowledgement or a mechanism similar to the one described in
FIG. 7a. During the ambiguity time, the assignments for UEs having not
yet acknowledged their switch to U-PDCCH may be sent both on the PDCCH
and the U-PDCCH, as an example.

[0121] It is noted that with the operations shown in FIG. 7b, the UEs
monitoring the U-PDCCH may not be affected by the switch since the SIB
assignment was sent in the common search space of the PDCCH region only,
unless, of course, the same or similar SIB assignment was sent in the
U-PDCCH control region. It is further noted also that some individual
overrides are possible for UEs. In such a case, the eNB may send a
message to a UE or a particular group of UEs to instruct it (or them)
regarding which control channel region to monitor.

[0122] In the operations described in FIG. 7b, the SIB message may be
broadcasted to all UEs monitoring the PDCCH control region, and, by
default, the UEs are switched. It is of course possible to use a
different broadcasting mechanism other than sending a SIB to instruct the
UEs of the switch. It may also be possible to restrict the switching to a
given group of UEs by, e.g., creating a multicast group, and sending the
switching indication to the multicast group only. Alternatively, the SIB
may comprise an indication to switch for only a subset of UEs. As an
example, this could be done by instructing only UEs having their UE Radio
Network Temporary Identifier (RNTI) ending up in a specified digit (or
some other specified value) to switch.

[0123] For some carriers, such as an extension carrier without PDCCH,
U-PDCCH may be the default, for example. The use of a control message on
a SIB may be useful if switching occurs frequently. Robustness may be
added by having the UE sending an acknowledgement of receipt of the
control message.

[0124] Blind switching may be used by the UE to switch its monitoring of
the PDCCH to the U-PDCCH and vice-versa. With blind switching, signaling
from the eNB may not be required. In blind switching, the UE may monitor
both the U-PDCCH and the PDCCH and can receive its assignment from either
control channel. Blind switching may be used in conjunction with a
reduction in search space to help reduce a number of blind decodings that
the UE performs. For instance, the common search space may be restricted
to the PDCCH control region only, and the U-PDCCH control region may have
the same number of possible candidates as the dedicated PDCCH search
space.

[0125] Implicit switching may also be used to cause the UE to switch its
monitoring of the PDCCH to the U-PDCCH and vice-versa. As an example,
implicit switching may be based on a power level monitored by the UE. The
UE may also report the power level to the eNB. The UE may switch
automatically when the power level meets a threshold, which may be
provided to the UE during initial attachment or during operations. The
threshold may also be sent by, e.g., higher layer signaling, or may be
broadcasted.

[0126] FIG. 8 illustrates a flow diagram of operations 800 in a UE as the
UE participates in implicit switching. Operations 800 may be indicative
of operations occurring in a UE, such as UE 110 and UE 120, as the UE
participates in implicit switching according to a specified threshold.

[0127] Operations 800 may begin with the UE measuring the link quality
(block 805). As an example, the UE may measure the link quality of a link
between itself and an eNB that is serving the UE. As an alternative
example, instead of the link quality, the UE may measure an error rate or
a metric of the link, such as a data rate, a bit rate, and the like. The
UE may send the measured link quality to the eNB (block 810). The UE may
compare the measured link quality to a threshold, which may be sent
directly to the UE or broadcast to the UE (block 815). If the link
quality is above (or, alternatively, below) a threshold as indicated by
`Y`, the UE may monitor the PDCCH region until it may be told to stop
monitoring the PDCCH or until the UE measures the link quality and the
newly measured link quality indicates to the UE to stop monitoring the
PDCCH (block 820). If the link quality is below (or, alternatively,
above) a threshold as indicated by `N`, the UE may monitors the U-PDCCH
region until it may be told to stop monitoring the U-PDCCH or until the
UE measures the link quality and the newly measured link quality
indicates to the UE to stop monitoring the U-PDCCH (block 825). It is
noted that the relationship between the measured link quality and the
threshold and how the PDCCH or the U-PDCCH is selected may depend on the
threshold. As an example, with a first threshold, if the measured link
quality is above the first threshold then the UE may monitor the U-PDCCH.
However, with a second threshold, if the measured link quality is above
the second threshold then the UE may monitor the PDCCH.

[0128] FIG. 9 illustrates a flow diagram of operations 900 in an eNB as
the eNB participates in implicit switching. Operations 900 may be
indicative of operations occurring in an eNB, such as eNB 105, as the eNB
participates in implicit switching according to a specified threshold.

[0129] Operations 900 may begin with the eNB receiving a link quality
report from the UE (block 905). The eNB may compare a link quality in the
link quality report to a threshold (block 910). As discussed above,
instead of the link quality report, the eNB may receive an error rate
report or a metric report, such as a data rate, a bit rate, and the like.
If the link quality is above (or, alternatively, below) a threshold as
indicated by `Y`, the eNB may send assignments for that particular UE in
the PDCCH region until the eNB decides to stop using the PDCCH or until
the eNB receives another link quality report from the UE (block 915). If
it is below (or, alternatively, above) the threshold as indicated by `N`,
the eNB may send assignments for that particular UE in the U-PDCCH region
until the eNB decides to stop using the PDCCH or until the eNB receives
another link quality report from the UE (block 920). It is noted that the
relationship between the measured link quality and the threshold and how
the PDCCH or the U-PDCCH is selected may depend on the threshold. As an
example, with a first threshold, if the measured link quality is above
the first threshold then the UE may monitor the U-PDCCH. However, with a
second threshold, if the measured link quality is above the second
threshold then the UE may monitor the PDCCH.

[0130] Measured link quality may be any indicator of the quality of the
communications link such as: signal-to-interference plus noise-ratio,
signal to interference ratio, signal to noise ratio, received power
level, received interference level, and the like. In addition, in order
to make the process more robust, there might be an acknowledgement
process when the switching occurs to make sure that the eNB and UE are
sending and/or monitoring the right region. As an example, the measured
link quality may be reported using the existing CQI/PMI/RI reporting
mechanism.

[0131] Furthermore, instead on being valid until the next link quality
report is sent (or received), the monitoring of a given control region
(PDCCH (i.e., the first control region) or U-PDCCH (i.e., the second
control region)) may be valid for a given time known a priori by both the
UE and the eNB. After that time, the UE may fall back to monitoring a
known (or default) control region, such as the PDCCH control region.
Mechanisms to help prevent a ping pong effect wherein the power level is
near the threshold and causes the UE to repeatedly switch its monitoring
of the control channel may be used. As an example, mechanisms used to
prevent the ping pong effect in handover situations may also be used in
control channel switching.

[0132] Control channel assignments may also be made on a
subframe-by-subframe basis. As an example, some subframes may be
predefined or configured using higher layer signaling to convey which
control channel the UE should be monitoring. The assignment may be made
on a per UE basis or UE group basis. On a particular subframe, the UE
knows which control channel to detect, either the PDCCH or the U-PDCCH,
for example. As an example, the subframes of a frame or a plurality of
subframes are divided by the eNB into a plurality of subsets. In one
illustrative example, two subsets may be used: S1 and S2. On subset S1,
the assignments are sent in the PDCCH control region only and on subset
S2, the assignments are sent in the U-PDCCH control region. The UE
monitors the control region according to the subset.

[0133] FIG. 10 illustrates a flow diagram of operations 1000 in an eNB as
it participates in subframe-by-subframe control channel assignments.
Operations 1000 may be indicative of operations occurring in an eNB, such
as eNB 105, as the eNB participates in subframe-by-subframe control
channel assignments.

[0134] Operations 1000 may begin with the eNB determining assignments for
the UEs scheduled for that particular subframe (block 1005). As an
example, the assignments for the UEs may be generated by the eNB,
computed by the eNB, extracted from a message or information received by
the eNB, retrieved from a memory, specified by a technical standard,
predetermined by an operator of the communications system, and the like.
In blocks 1010 and 1011, the eNB may determine whether the subframe
belongs to subset S1 or subset S2. If the subframe belongs to subset S1,
the eNB may send the assignments in the PDCCH control region (block
1015). If the subframe belongs to subset S2, the eNB may send the
assignments in the U-PDCCH control region (block 1020). It is noted that
the above discussion of which subset corresponds to which control channel
are merely illustrative examples and that other subset to control channel
associations may be possible.

[0135] FIG. 11 illustrates a flow diagram of operations 1100 in a UE as it
participates in subframe-by-subframe control channel assignments.
Operations 1100 may be indicative of operations occurring in a UE, such
as UE 110 and UE 120, as the UE participates in subframe-by-subframe
control channel assignments.

[0136] Operations 1100 may begin with the UE determining a number of the
subframe (block 1105). As an example, the number of the subframe may be
used to determine which subframe subset the subframe belongs. In blocks
1110 and 1111, the UE may determine whether the subframe belongs to
subset S1 or subset S2. The UE may then monitor the control region based
on the subset determination in blocks 1110 and 1111. As an example, if
the subframe belongs to subset S1, the UE may monitor the PDCCH region
(block 1115). While, if the subframe belongs to subset S2, the UE may
monitor the U-PDCCH region (block 1120).

[0137] As another illustrative example, the subframes of a frame or a
plurality of subframes may be divided into three subsets, S1, S2, and S3,
where the PDCCH control region is used for the subframes belonging to
subset S1, the U-PDCCH control region is used for the subframes belonging
to subset S2, and for the subframes belonging to subset S3, the eNB may
not transmit any resource assignments in those subframes, and the UE may
not assume that it will get an assignment on such a subframe. In another
illustrative example, the subframes of a frame may be divided into three
subsets, S1, S2, and S3, where the PDCCH control region is used for the
subframes belonging to subset S1, the U-PDCCH control region is used for
the subframes belonging to subset S2, and for the subframes belonging to
subset S3, both the U-PDCCH and PDCCH control regions are present. The
presence of the subsets as well as their configuration may be signaled
using RRC signaling, OAM signaling, may be broadcasted on e.g., a SIB,
and the like. A specification of which subframes may be assigned which
control channel may be based on information, such as ABS assignments. As
an example, a specific UE may be assigned to monitor subframes pertaining
to a single subset only, so it only has to monitor either the PDCCH or
the U-PDCCH control region. Alternatively, a UE may be assigned to
monitor subframes of more than one subset.

[0138] Control channel assignments may also be dynamically triggered. As
an example, an indicator or a bit in a PDCCH (or in a U-PDCCH) may
indicate that the UE should also look in the U-PDCCH (or in the PDCCH)
control region. An indicator in a PDCCH may indicate to the UE that it
should also search in the U-PDCCH control region. Similarly, an indicator
in a U-PDCCH may indicate to the UE that it should also search in the
PDCCH control region. Similarly, a multi-bit indicator may indicate that
the UE should search in the PDCCH control region, the U-PDCCH control
region, or both the PDCCH and the U-PDCCH control regions.

[0139] FIG. 12 illustrates a flow diagram of operations 1200 in an eNB as
the eNB uses dynamically triggered control channel assignments.
Operations 1200 may be indicative of operations occurring in an eNB, such
as eNB 105, as the eNB uses dynamically triggered control channel
assignments.

[0140] Operations 1200 may begin with the eNB determining whether it will
transmit in the U-PDCCH region (block 1205). If the eNB determines that
it will transmit in the U-PDCCH region (for example `Y`), the eNB may set
an indicator to a first value, such as `1` (block 1210). Otherwise (for
example `N`), the eNB may set the indicator to a second value, such as
`0` (block 1215). The eNB may then send the indicator in the common
search space of the PDCCH region (block 1220). The eNB may determine
whether the U-PDCCH and the PDCCH control regions are used (block 1225).
If both regions are used (for example `Y`), the eNB may then determine
which assignments are to be sent on the PDCCH region and which
assignments are to be sent on the U-PDCCH region, and sends them
accordingly (block 1230). Otherwise (for example `N`), the eNB may send
the assignments in the PDCCH control region only (block 1235). It is
noted that by extension, a multi-bit indicator may be used to enable the
eNB to transmit in the PDCCH control region, the U-PDCCH control region,
or both the PDCCH control region and the U-PDCCH control region.

[0141] FIG. 13 illustrates a flow diagram of operations 1300 in a UE as
the UE participates in dynamically triggered control channel assignments.
Operations 1300 may be indicative of operations occurring in a UE, such
as UE 110 and UE 120, as the UE participates in dynamically triggered
control channel assignments.

[0142] Operations 1300 may begin with the UE monitoring the common search
space of the PDCCH control region (block 1305). The UE may perform a
check to determine if the indicator is present (block 1310). If the
indicator is present, the UE may examine the indicator to determine a
value of the indicator. If the indicator is set to the first value (for
instance `1` to indicate the presence of the U-PDCCH), the UE may monitor
both the U-PDCCH and the PDCCH regions (block 1320). If the indicator is
set to a second value (for instance `0` to indicate the absence of the
U-PDCCH), the UE may monitor the PDCCH control region only (block 1325).
If there is no indicator (block 1310), the UE may monitor the PDCCH
control region (block 1325). It is noted that by extension, a multi-bit
indicator may enable the UE to monitor the PDCCH control region, the
U-PDCCH control region, or both the PDCCH control region and the U-PDCCH
control region.

[0143] An eNB may determine when to transmit the U-PDCCH (or both the
PDCCH and the U-PDCCH) on a frame-by-frame basis, for an extended period
of time (such as a number of frames), and the like. The indicator may be
sent in both the U-PDCCH and PDCCH common search space regions. The
indicator may comprise one or more bits. Alternatively, the indicator may
comprise one or more states of another control field, such as unused
combinations of bits in an existing control field. Additionally, if an
absence of the indicator may indicate that no U-PDCCHs are transmitted in
the U-PDCCH control region, or that no assignment is transmitted in a
particular subframe, then the indicator may not necessarily be sent in
the common search space of the PDCCH region, but the indicator may
consist of one bit that is transmitted on the PCFICH, for example.

[0144] In order to avoid requiring the UEs monitor both the PDCCH and
U-PDCCH control regions, the indicator may be expanded to indicate
monitoring assignments for a group of UEs. As an example, the indicator
may indicate that assignments for a group of UEs are in the U-PDCCH
control region. The expansion may be implemented, for example, by sending
a group ID in the indicator, e.g., sending the last digit of the UE RNTI,
for UEs that are to monitor the U-PDCCH control region. In addition, the
indicator may be overridden by higher layer and/or dedicated signaling.

[0145] Furthermore, during a handover, information regarding which control
channel and/or control region the UE should monitor at a handover target
may be conveyed during a message exchanged during the handover process.

[0146] An example communications system design may be as follows:

[0147] Any eNB is capable of transmitting the PDCCH and/or the U-PDCCH.
While previous release (e.g., Release-10 or earlier) UEs only monitor the
PDCCH, new release (i.e., the releases supporting U-PDCCH, e.g.
Release-11 UEs or later) UEs may monitor both channels. The ability of a
UE to monitor U-PDCCH may be mandatory, may be mandatory but only tested
if a feature group indicator (FGI) is set to indicate that it is tested,
or a UE capability where the UE may or may not have the ability;

[0148] UE capable of monitoring the U-PDCCH may first look at the PDCCH
common search space. Each UE may be assigned to monitor either the PDCCH
and/or the U-PDCCH by RRC signaling;

[0149] UEs may monitor the U-PDCCH, but first decode the PDCCH common
search space. In the PDCCH common search space region, there may be an
indicator (e.g., one bit) to indicate whether the U-PDCCH is present or
not. In the PDCCH common search space, there may also be a Downlink
Control Information (DCI) format 3B message to indicate the U-PDCCH
characteristics;

[0150] In addition, the UE may find a message to indicate a
reconfiguration of the search space for the U-PDCCH. If no message is
present, the UE may assume that the UE-specific search space is the same
as before. If there is a message, the UE may immediately use the new
configuration;

[0151] The U-PDCCH starts on the symbol immediately following the PDCCH;
and

[0152] If the UE receives an indication to monitor the U-PDCCH, the UE may
attempt blind decoding on its UE-specific U-PDCCH search space with the
U-PDCCH characteristics. If the UE does not receive the indication, the
UE may assume that it has no assignment, and does not need to perform
additional blind decodes on the PDCCH region.

[0153] FIG. 14 illustrates a communications device 1400. Communications
device 1400 may be used to implement various ones of the embodiments
discussed herein. As shown in FIG. 14, a transmitter 1405 is configured
to transmit information and a receiver 1410 is configured to receive
information.

[0154] A UE controller 1420 is configured to determine which control
channel(s) a UE is to monitor. The determination may be based on a number
of factors, such as UE capability, communications system capability, and
the like. An assignment unit 1425 is configured to assign a UE to monitor
a control channel(s). Assignment unit 1425 may select a location for the
control channel(s), as an example, assignment unit 1425 may select a
control channel type for the control channel that the UE is assigned to
monitor. For example, assignment unit 1425 may assign a UE to monitor a
PDCCH, a U-PDCCH, or both PDCCH and U-PDCCH. A search space controller
1430 is configured to specify a search space or a set of search spaces
(possibly out of a number of possible search spaces) where a UE may
search to find a U-PDCCH. A parameter unit 1435 is configured to select
and/or assign communications parameters, such as rank, coding rate,
modulation scheme, antenna port, and the like, to a UE. A signaling unit
1440 is configured to generate messages and/or indications to be
transmitted to a UE, where the messages and/or indications convey control
information, channel assignments, parameters, and the like. Signaling
unit 1440 is configured to modulate information to be transmitted, as
well as map the modulated information onto resources, such as resource
elements, resource blocks, control channel elements, and the like. A
resource grant unit 1445 is configured to grant network resources to UEs.
A memory 1450 is configured to store information, such as channel
assignment, parameters, etc.

[0155] The elements of communications device 1400 may be implemented as
specific hardware logic blocks. In an alternative, the elements of
communications device 1400 may be implemented as software executing in a
processing unit such as processor (e.g., microprocessor or digital signal
processor), controller, application specific integrated circuit, and the
like. In yet another alternative, the elements of communications device
1400 may be implemented as a combination of software and/or hardware.

[0156] As an example, transmitter 1405 and receiver 1420 may be
implemented as a specific hardware block, while UE controller 1420,
assignment unit 1425, search space controller 1430, parameter unit 1435,
signaling unit 1440, and resource grant unit 1445 may be software modules
executing in a microprocessor or a custom circuit or a custom compiled
logic array of a field programmable logic array.

[0157] FIG. 15 illustrates a communications device 1500. Communications
device 1500 may be used to implement various ones of the embodiments
discussed herein. As shown in FIG. 15, a transmitter 1505 is configured
to transmit information and a receiver 1510 is configured to receive
information.

[0158] A blind detector 1520 is configured to detect transmissions by
search a search space for the transmissions. A search space controller
1525 is configured to control the searches made by communications device
1500 based on search space(s) specified by an eNB controlling the
communications device 1500. A channel selector 1530 is configured to
select a control channel to monitor based on instructions from the eNB,
power measurements, performance metrics, a location indicator, control
channel type, and the like. A parameter unit 1535 is configured to
process communications parameters provided by the eNB. Signaling unit
1540 is configured to demodulate information from resources, such as
resource elements, resource blocks, control channel elements, and the
like. A memory 1545 is configured to store information, such as channel
assignment, parameters, etc.

[0159] The elements of communications device 1500 may be implemented as
specific hardware logic blocks. In an alternative, the elements of
communications device 1500 may be implemented as software executing in a
processing unit such as processor (e.g., microprocessor or digital signal
processor), controller, application specific integrated circuit, and the
like. In yet another alternative, the elements of communications device
1500 may be implemented as a combination of software and/or hardware.

[0160] As an example, transmitter 1505 and receiver 1520 may be
implemented as a specific hardware block, while blind detector 1520,
search space controller 1525, channel selector 1530, parameter unit 1535,
and signaling unit 1540 may be software modules executing in a
microprocessor or a custom circuit or a custom compiled logic array of a
field programmable logic array.

[0161] FIG. 16 illustrates locations of exemplary U-PDCCH within a new
control region 1600. As shown in FIG. 16, a U-PDCCH 1601 may span a range
of frequencies within a data region. While U-PDCCH 1602 may include RBs
in a first slot and in a second slot. U-PDCCH 1603 may include RBs in the
first slot and U-PDCCH 1604 may include RBs in the second slot.

[0162] A time location of the U-PDCCH may also be defined. For example,
the R-PDCCH as defined for 3GPP LTE Release-10 always starts on the
fourth symbol (symbol #3 using zero-based numbering). It may be desirable
to have the U-PDCCH starting as early as symbol #0. This could occur, for
an example, in a carrier designated as an extension carrier, which does
not have a PDCCH region. In such as case, cross carrier scheduling or
U-PDCCH would be used, with switching possible between the PDCCH
performing the cross carrier scheduling and the U-PDCCH behaving as
described in the previous section, if both the U-PDCCH and PDCCH control
regions are present. Another possibility may be to use a Physical Control
Format Indicator Channel (PCFICH) to obtain PDCCH length. As an example,
an eNB may transmit both the PDCCH and the U-PDCCH, with the U-PDCCH
starting after PDCCH if both occupy a single subframe or with the U-PDCCH
starting as early as at symbol #0 if there is no PDCCH in the subframe.

[0163] FIG. 17 illustrates a flow diagram of UE operations 1700 in
searching for U-for a U-PDCCH using a PCFICH. UE operations 1700 may be
indicative of operations occurring in a UE, such as UE 110 and UE 120, as
the UE uses a PCFICH to search for a U-PDCCH.

[0164] UE operations 1700 may begin with the UE determining a temporal
duration (e.g., a Control Format Indicator (CFI) value) of the PDCCH
control region from the PCFICH (block 1205). The UE may determine the
starting point of the U-PDCCH control region based on the end of the
PDCCH control region (block 1210). For instance, the U-PDCCH control
region may start on the symbol immediately following the PDCCH control
region, or one or more symbols later (e.g., after an offset). This offset
can be explicitly stated in the standard or may be provided by higher
layer signaling, e.g., RRC or SIB. However, if there is no PDCCH control
region, the U-PDCCH control region may start on the symbol immediately
following the start of the subframe.

[0165] Advantageous features of embodiments of the disclosure may include:
a method for a wireless network node to send resource grants for a given
subframe to a plurality of wireless nodes in a transmission system using
multicarrier modulation, the method comprising: determining two control
regions, wherein a first control region occupies one or time symbols at
the beginning of the frame, and wherein a second control region occupies
some of the resources in a remainder of the frame; transmitting resource
allocation grants to wireless nodes in either of the control region; and
sending to each wireless node an indication of which control region to
monitor.

[0166] The method could further include, wherein the indication is sent by
higher layer signaling. The method could further include, wherein the
wireless network node receives an acknowledgment after having sent the
indication of which control region to monitor. The method could further
include, wherein the resource grants for a particular wireless node are
sent on both control regions until an acknowledgement is received. The
method could further include, wherein the acknowledgement is implicitly
derived from a packet acknowledgment message from the remote wireless
node.

[0167] The method could further include, wherein the indication to switch
is sent on a system information block. The method could further include,
wherein the indication to switch comprises an indication to switch for a
subset of users. The method could further include, wherein the subset of
users is indexed by their UE RNTI. The method could further include,
wherein the indication to switch is implicitly derived from a link
quality reported by the wireless users.

[0168] The method could further include, wherein the link quality report
comprises at least one of the following: signal to interference plus
noise ratio, signal to interference radio, received power level, received
interference power level. The method could further include, wherein the
indication to switch is dependent on a subframe index. The method could
further include, wherein the indication to switch is sent on a subframe
by subframe basis. The method could further include, wherein the
indication to switch is sent in a common search space region of a PDCCH
region.

[0169] The method could further include, wherein the indication to switch
comprises an indication to switch for a subset of users. The method could
further include, wherein the subset of users is indexed by their UE RNTI.
The method could further include, wherein the resource grants for a
particular wireless node are sent on both control regions for a specified
time period. The method could further include, wherein a timer is used to
measure a duration of the determining the two control regions.

[0170] Advantageous features of embodiments of the disclosure may include:
a method for wireless node operations, the method comprising: monitoring
a first control region and a second control region, wherein a first
control region occupies one or time symbols at a beginning of a frame,
and wherein a second control region occupies some of the resources in a
remainder of the frame; receiving an indication of which control region
to monitor; and monitoring the first control region or the second control
region responsive to the indication.

[0171] The method could further include, wherein the indication is
received in higher layer signaling. The method could further include,
further comprising sending an acknowledgement after receiving the
indication. The method could further include, wherein resource grants for
the wireless node are sent on both control regions until an
acknowledgement is received by a wireless network node sending the
indication. The method could further include, wherein the acknowledgement
is implicitly derived from a packet acknowledgement message received by
the wireless network node.

[0172] The method could further include, wherein the indication is
received in a system information block. The method could further include,
wherein the indication comprises an indication intended for a subset of
wireless nodes. The method could further include, wherein the subset of
wireless nodes is indexed by their UE RNTI. The method could further
include, wherein the indication is implicitly derived from a link quality
report sent by the wireless node.

[0173] The method could further include, wherein the link quality
comprises a signal to interference plus noise ratio, a signal to
interference radio, a received power level, a received interference power
level, or combinations thereof. The method could further include, wherein
the indication is dependent on a subframe index. The method could further
include, wherein the indication is received on a subframe by subframe
basis. The method could further include, wherein the indication is
received in a common search space region of a PDCCH region.

[0174] The method could further include, wherein the indication comprises
an indication to switch for a subset of wireless nodes. The method could
further include, wherein the subset of users is indexed by their UE RNTI.

[0175] Advantageous features of embodiments of the disclosure may include:
a wireless network node comprising: a search space control unit
configured to determine control regions, wherein a first control region
occupies one or time symbols at the beginning of a frame, and wherein a
second control region occupies some of the resources in a remainder of
the frame; a resource grant unit coupled to the search space control
unit, the resource grant unit configured to grant network resources to
wireless nodes in either of the first control region or the second
control region; and a transmitter coupled to the search space control
unit, the transmitter configured to transmit an indication of either the
first control region or the second control region to monitor.

[0176] Although the present disclosure and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing from
the spirit and scope of the disclosure as defined by the appended claims.